The present invention relates to a process for forming a thread-reserve winding on a bobbin tube of a spinning machine, in which the thread is drawn off continuously from the spinning machine by means of a pair of draw-off rollers containing a pressure roller. The thread is conveyed into a thread-suction device before the start of the thread-reserve winding. It is then brought into a thread transfer position, in which it intersects the plane of rotation of a thread-catching device rotating together with the bobbin tube where it is grasped by the said thread-catching device and is then cut off.
In producing bobbins filled with thread, it is generally customary before the start of the bobbin build-up first to wind a thread reserve on one end of the bobbin tube, in order subsequently to be able to join together the thread ends of individual complete bobbins and thus draw off the yarn uninterruptedly from a plurality of bobbins. At the same time, the thread reserve has to be wound onto the bobbin tube so securely that, when the bobbin is handled, it does not become loose or slip off from the tube and thus become a disturbing factor.
However, in a spinning machine, for example on open-end spinning machines, in which the thread is drawn off continuously and delivered to the winding-on device, difficulties arise in meeting the requirement that the thread reserve should be wound onto the bobbin tube securely. These difficulties occur because the thread is not traversed during the formation of the thread-reserve winding, and therefore the length of the thread wound on the bobbin tube during formation of the thread reserve winding is less than the length of the thread delivered from the spinning device by the draw-off rollers. Consequently, between the bobbin tube and the pair of draw-off rollers drawing off the thread from the spinning machine, there is no thread tension necessary for ensuring that the thread reserve is wound on securely.
A solution to this problem in an open-end spinning machine is described U.S. Pat. No. 4,501,116 on which the invention is based. According to this known proposal, the excess length of supplied thread, which occurs during the formation of the thread-reserve winding, is stored immediately in a pneumatic thread store and is used up again, at the start of the bobbin build-up during the normal winding of the bobbin as a result of the traversing of the thread over the length of the tube. However, in addition to the additional outlay caused by a pneumatic thread store and an increased air consumption, this process is also unsatisfactory as regards the tautness of the thread-reserve winding.